Consider dropping md2po, direct use of md files by Weblate

**Short description**: Weblate now supports md files. It might be worth feeding Weblate with markdown files directly, without having to go through md2po.

**Location**: everywhere

**Why have this**: Dropping one link in the translations chain might make things less complex.

**More info**: https://docs.weblate.org/en/weblate-5.0/formats/markdown.html